During operation of a centrifugal separator of this kind the components in the liquid mixture which is supplied to the separating chamber via the inlet chamber of different densities are separated, whereby the specifically heaviest components are being accumulated in the radially outermost portion of the separating chamber. The accumulated volume of the heavier component gradually builds up radially inwards and thus eventually reaches a radial level at which part of the heavier component is entrained in the flow of a specifically lighter component radially inwards in the separating chamber and further out of the separating chamber via the radially inner outlet, thereby impairing the separation results. In order to be able to continue the centrifugal separation without impaired separation results, a predetermined volume of the contents of the separating chamber is intermittently discharged from the separating chamber via the radially outer outlet at regular intervals of time or when an impairment of the separation results is detectable.
The intermittent discharge in such cases is controlled by equipment which has a supervision unit comprising a device adapted to initiating the intermittent discharge of the predetermined volume while the separated component is discharged from the separating chamber, and to stopping the discharge and starting a resumption of normal separation in the separating chamber. The supervision unit often further comprises a time-measuring means, a memory and an indicating means.
In the German patent specification DE 41 11 933 C1 there is proposed a method of supervision in a centrifugal separator whereby a desired partial volume of the contents of the separating chamber is discharged intermittently in a correct manner. According to that method, the power consumption of the electric motor which drives the rotor of the centrifugal separator is measured immediately before an intermittent discharge, followed by measurement of the power consumption increase caused by the discharge. The difference between the resulting two measured values is compared with the value which corresponds to a power consumption increase due to a correct intermittent discharge, and deviations from that value are evaluated in a control unit.
However, the power consumption will also vary for other reasons, which means that an increase in it will not always be representative of a supervised discharge. The method also involves extra measuring equipment, which makes the supervision expensive.
In the Swedish patent specification SE 503 017 there is disclosed another method of supervision whereby a desired partial volume of the contents of the separating chamber is discharged intermittently in a correct manner and operation is supervised by measuring the time it takes for an outflow via the central outlet to be indicated again after it has ceased temporarily during an intermittent discharge. Although the method has great possibilities, it is complicated and expensive for some applications.
An object of the present invention is to provide a simple method for supervising a centrifugal separator of the kind described in the introduction, which method makes it possible reliably and at low cost to verify mainly that the initiated intermittent discharge of the predetermined volume has actually taken place.